Question

Scdoris has been born with _______medical condition that limits her vision.

Answer 1

You need a slight stop there to collect your thoughts, especially when the next word is achromatopsia. That makes D wrong.

If you use B, " A medical condition that limits her vision" is not a sentence. So B shouldn't be the answer. Fragments are used by very good writers usually in fiction, and this statement is not part of something that is fictional.

A semicolon separates two equal clauses. You can think of it as meaning "and" or even "but" sometimes. You have the same problem with C as you do with B. So C is not correct.

That leaves us with A. That should be your answer.You need a pause of some kind and that pause is proved by the comma. The sentence is not a run on sentence just one in need of a pause in the middle.